The legislation is expected to come before the upper house in coming days, where it will likely garner enough support to become law.

If it passes, the Crimes Act will be changed to specify that consent to sexual activity must be communicated by words or action, rather than assumed.

If consent isn't communicated, the other person could be guilty of sexual assault.

The bill also spells out that just because someone doesn't physically or verbally resist a sexual activity, it does not mean they've consented.

Attorney-General Mark Speakman described the reforms as "a basic matter of respect" as he introduced the bill to the lower house last month.

"No one should assume someone is saying 'yes' just because they do not say 'no' or do not resist physically," he said.

"People are entitled to expect that if someone wants to have sex with them, then that other person will ask -- and that if the first person has not said something or done something to communicate consent, then the other person will take further steps to ascertain consent."

The bill won support in the lower house on Wednesday evening, after several amendments moved by the Greens and Labor failed.

Greens spokesperson for women Jenny Leong called the development a significant achievement for sexual assault advocates and survivors.

"This is a significant moment. This is a very significant reform," Ms Leong said in a statement on Thursday.

"The Bill puts victim-survivors at the heart of the law, and removes rape myths and assumptions from the Crimes Act.

"It removes the patriarchal assumption that anyone is entitled to sex without the active, enthusiastic consent of the other person."

Mr Speakman says the bill isn't just about holding perpetrators to account, but changing social behaviour.

The government plans to roll out extensive community education to make sure people understand how the affirmative model of consent works.

The bill also updates the definitions of 'sexual intercourse', 'sexual touching' and 'sexual act'.

Australian Associated Press